If you've ever tried to book a big house for a knees-up, you'll appreciate how difficult it can be. 'We don't want people vomiting on our new carpet.' 'No, we don't sleep more than 20 people (even though we've got 75 bedrooms), because of the mess big groups make.' Either that, or they quote you a five-figure sum.

So there was lots of 'goodonyer' and backpatting when my friend Sally nailed down an affordable big house for the weekend to celebrate her partner's fortieth birthday. Not only would it sleep more than 20, but we could have a party on the Saturday night for as many as would come.

There was of course a drawback. Whichever way you phrased it, it didn't sound alluring. Doncaster. Near Doncaster. Just 11 miles from Doncaster.

We arrived at Hermeston Hall minutes before the birthday boy, Rob, crawled out of a chauffeur-driven Rolls in his denim jacket with a bemused look on his face.

'Fletcher' the betailed butler, gave a deep bow and a tall blond maid in black and white curtsied. Scullery maids, cleaners and waitresses bowed and scraped as Rob walked up the stone steps through the huge oak doors.

A few whispers to the other guests revealed that the line-up of servants, chauffeur and butler were not actors or students hired for the occasion, but the owners of the house and their mates.

We were staying, we found, in the home of the 'chauffeur' Tim and 'pantry maid' Jayne. That was their green shiny Rolls parked outside. That was their tennis court in the front garden. And Rob and Sally were going to be sleeping in their beds (the owners having decamped to a far distant wing of this mansion for the weekend).

A 50-room house is quite something for a party. It became clear - and understandable - why the owners normally live in just three rooms (the living room, kitchen and their en-suite bedroom). These are the warmest, or rather, the only warm rooms in the 1880-built mansion.

In fact, half of it seemed derelict or full of rubbish. Open a door, and ladders, lilos and bedding would come tumbling down. Open another and there was the biggest billiard table you've seen. Another had a dusty, six-track Scalextric set and another was full of musical instruments. Others were piled with cardboard boxes.

We had been assigned 'the Chinese room' (something to do with the cushion covers). This was at the end of a long, dark, chilly corridor, about a five-minute walk from the two Victorian bathrooms which were to be shared between most of the 24 guests. Both had huge throne-style toilets, with a long shaky chain and dodgy plumbing. The bath looked as if it would take a week to fill. There were no showers and the water took hours to heat. Luckily there was a large chamber pot under our bed and we'd had a shower before coming.

By 8pm most of the 24 guests were quaffing champagne in the lounge. Jayne and the suntanned butler (normal job: company director) filled drinks and offered canapes while Tim (who'd done a quick change from the chauffeur outfit) swanned around in a velvet jacket. 'These things are great, as long as I can keep off the booze,' he confided, taking a big glug from his glass.

I noticed more guests in the room than 24. This was because a couple of the couples (the American contingent) had discovered the bathroom situation in advance and booked into local hotels. Life without a shower? No way.

'Dinner is served,' announced Fletch, banging a large gong. We filed into the dining room - a chandeliered affair with a long table with cut glass, silver cutlery, big candlesticks and lots of velvet, all very Titanic and all very unmatched (the owners had begged or borrowed to get enough crockery and cutlery for the occasion).

Waiters and waitresses swarmed around pouring us large quantities of wine and bringing in course after course, from salmon pasties and tarragon chicken to creamy desserts and cheeseboard.

I was first at breakfast next morning (only reason: pregnant and teetotal). Jayne was running around the Aga-warmed kitchen (having replaced the maid outfit with jeans and jumper) boiling eggs and making pots of tea. Tim looked hung over.

'Why do you do these events?' I asked.

'We hate to see a place like this standing empty, we like the money and we have great fun doing them,' said Tim (who's in the handmade brick business). They moved here from Northampton three years ago after buying the property for the same price as a two-bedroom flat in Fulham.

'It's great. We get to lord it up and other people have fun too!' he beamed.

'I wouldn't say "lording it up" when I'm the scullery maid and you're the chauffeur!' piped up Jayne, rifling through the cupboards for the Marmite.

They've held everything from weddings to singles parties at the house in recent months, sometimes using outside caterers and marquees, sometimes doing it themselves, and making themselves scarce, or visible, as required.

The concept of the owners being around might terrify some guests - wouldn't they be fussing about every drop of red wine on the carpet, or smashed ornament? Not here. When my daughter Hanna, aged three, bumped into a huge China dog in the hallway, breaking its paw in two, Tim's response was: 'Oh don't worry about that - I've glued it on once already.'

Tim and Jayne's relaxed attitude to strangers running drunkenly around their mansion seemed to have no limits. The house would go from being extremely civilised (such as on the Saturday night when the Titanic room had been transformed for a buffet with poached salmon, coronation chicken, roast ham, salads and potatoes, with Fletch and Co serving and pouring the drinks) to a riot. At 5am on Sunday people were still boogying around the lobby aided by four DJs from Sheffield who'd set up shop under the staircase next to the grand piano.

Up at dawn on Sunday, I found a drunken body in a leather jacket asleep on three cushions on the dining room floor. In the once-regal lounge were half a dozen corpses reeking of alcohol and snoring from leather sofas. There was even a VW Campervan parked outside with a pile of bodies inside it. But by 11am, the bodies had risen to play tennis in their dressing gowns on the front lawn court.

So, having got to the end of this you're probably wondering if I'm recommending Hermeston Hall or not. Storage heaters, no showers (apart from the ensuite in the master bedroom), the need to wear a fleece over your cocktail dress, dust, clutter and car-boot-sale furniture and fittings ...

Having organised a wedding four years ago and been to other weekend get-togethers, this is not a bad option. If you've ever rung a classified ad to rent a big house for the weekend and said the words 'stag party', or 'fortieth birthday party', you'll usually have found that the owners can't get you off the phone quick enough - or else they quote you £20,000 and ask for another few grand as a deposit in case of breakages.

But at Hermeston Hall, they'll quote you a tenth of that and ask if it's OK if they join in the party.